Highly volatile organic compounds, e.g., halogenated hydrocarbons such as trichloroethylene and tetrachloroethylene, aromatic compounds such as benzene, xylene and toluene, and aldehydes such as acetaldehyde and formaldehyde are industrially widely used as solvents, detergents, etc., and organic agricultural chemicals such as organic chlorine compounds and organic phosphorus compounds are used as insecticides, fungicides and herbicides in agricultural fields. Some of these organic compounds have toxicity or carcinogenicity for men or cause inhibition of growth and induction of malformation for animals and plants, and preparation, use and disposition of them are severely regulated. However, many of the above organic compounds are hardly decomposable, and those which have been abandoned or leaked under no severe control or those which have been used before issuance of regulations, such as DDT and BHC, remain in the environment. These compounds have polluted soil or underground water over a long period of time, and, furthermore, highly volatile matters discharged into atmosphere have polluted the atmosphere, which have caused serious social problems. Furthermore, recently, it has been reported that a part of organic compounds act as so-called endocrine disturbing substances (or environmental hormones) which inhibit generative power of animals and plants.
On the other hand, since nitrate and nitrite nitrogen-containing compounds have carcinogenicity, recently, discharge of them is severely controlled as water pollutants, and chemical industries and fertilizer industries are demanded to cope with the problems. Moreover, in agriculture, organic nitrogen compounds contained in fertilizers produce nitrate and nitrite nitrogen-containing compounds by biodegradation or oxidative decomposition in the fertilized soil, which not only pollute underground water and agricultural waste water, but also cause formation of acidic soil to inhibit rearing of crops. These are also serious problems.
As a method for remediating organic compounds in soil, it has been known to carry out the airlation of soil and collect gaseous components, followed by carrying out reduction decomposition using hydrogen as a reducing agent and platinum or palladium as a catalyst (for example, Isao Joko, “Environmental Catalyst Handbook”, (p. 134-138, the first edition, published from NTS Co., on Nov. 20, 2001, hereinafter referred to as “Non-Patent Document 1”). Moreover, there is known a method of directly introducing reducing agent or oxidizing agent into polluted soil to carry out reduction decomposition or oxidation decomposition of organic compounds, which is so-called in-situ remediation method. According to this method, metallic iron (e.g., U.S. Pat. No. 3,079,109 (pages 1-2), hereinafter referred to as “Patent Document 1”) or a composite compound of magnetite and metallic iron (e.g., JP-A-2002-317202 (page 1), hereinafter referred to as “Patent Document 2”) is used as a reducing agent, and potassium permanganate or hydrogen peroxide (e.g., JP-A-7-75772 (page 1), hereinafter referred to as “Patent Document 3”) is used as an oxidizing agent.
For remediating nitrate or nitrite nitrogen-containing compounds in waste water, there are known a method of reducing with hydrogen as in the treatment of the organic compounds, ion exchange method, reverse osmosis method, electrodialysis method, and biodegradation method using bacteria (e.g., pages 89-91 of Non-Patent Document 1). Furthermore, there is known a method of remediating nitrate nitrogen contained in waste water using a solid catalyst containing a metal compound such as titanium oxide or iron oxide and a noble metal catalyst such as platinum, palladium or nickel in the presence of a reducing agent with keeping waste water in liquid phase at a temperature of 120-370° C. under a pressure at which the waste water keeps liquid phase (e.g., JP-A-9-70589 (pages 1-8), hereinafter referred to as “Patent Document 4”). In the case of remediating nitrate or nitrite nitrogen-containing compounds in soil, the above in-situ remediation method is also applied, and metallic iron or sulfide is used as the reducing agent introduced into soil.